Colon, or large intestine, coloured barium X-ray. The colon starts at the caecum (centre left), where the small intestine (not seen) joins it. The finger-like appendix is seen below the caecum. The colon then ascends and crosses the abdomen, before descending on the opposite side (right). It then turns into the rectum (lower centre), where faeces is stored before expulsion through the anus (bottom centre). The bones of the pelvis (pale brown) are in lower frame, and the spine runs up centre. The colon has been highlighted on the X- ray by introducing a radio-opaque contrast medium (usually barium salts in liquid) into it. This is an important method of diagnosing colon disorders.